Here's a simplified version:
Small ship moves forward speed 1 = front of ship advances 2 lengths from previous spot.
Small ship moves forward speed 3 = front of ship advances 4 lengths from previous spot.
Large ship moves forward speed 1 = front of ship advances 3 small base lengths from previous spot.
Large ship moves forward speed 4 = front of ship advances 6 small base lengths from previous spot.
